“用于"循环未填充矩阵 [英] "for" loop is not populating the matrix
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问题描述
我正在用"for"循环计算每个点的角度.但是不知何故矩阵没有被填充.仅矩阵中的第一个元素填充了计算值.
I am calculating angles for each point with 'for' loop. But somehow the matrix is not populated as desirable. Only the first element in matrix is populated with calculated value.
w1 = c(-2.40154, -1.82937)
w2 = c(-2.079041, 101,0663)
xy = as.data.frame(coordinates(p))
angle = function (w1, w2 , p, ...) {
iterations = 2500
a = sqrt ((w1[1]-w2[1])^2 + (w1[2]-w2[2])^2)
tr <- matrix(ncol=1, nrow=iterations)
for (i in 1:iterations) {
b[i] = sqrt ((p$coords.x1[i]-w1[1])^2 + (p$coords.x2[i]-w1[2])^2)
c[i] = sqrt ((p$coords.x1[i]-w2[1])^2 + (p$coords.x2[i]-w2[2])^2)
tr[i,] = (acos ((b[i]^2 + c[i]^2 - a^2)/ (2*b[i]*c[i]))*180)/pi
print(tr)
}
return(tr)
}
t = angle(w1,w2,xy)
tr
仅获得第一个值.请更正代码.
tr
is getting only the first value. Please correct the code.
推荐答案
通常,您不想遍历一次执行一个索引的向量.相反,您想对向量进行整体操作.这将使您的代码更短,更高效:
Usually you don't want to loop through vectors performing one index at a time. You instead want to operate on the vectors as a whole. This will make your code both shorter and more efficient:
w1 = c(-2.40154, -1.82937)
w2 = c(-2.079041, 101,0663)
p <- data.frame(coords.x1=c(4, 5), coords.x2=c(6, 7))
angle <- function(w1, w2, p) {
a <- sqrt ((w1[1]-w2[1])^2 + (w1[2]-w2[2])^2)
b <- sqrt ((p$coords.x1-w1[1])^2 + (p$coords.x2-w1[2])^2)
c <- sqrt ((p$coords.x1-w2[1])^2 + (p$coords.x2-w2[2])^2)
return(matrix((acos ((b^2 + c^2 - a^2)/ (2*b*c))*180)/pi, ncol=1))
}
angle(w1, w2, p)
# [,1]
# [1,] 137.0681
# [2,] 135.7206
基本上,我所做的只是删除了 i
建立索引,您的代码按预期运行.
Basically all I did was remove the for loop and the indexing by i
and your code works as expected.
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